A brief summary from a quick dig I made into this paper: They did 3 different CRISPR targeted kncok-ins, that is, using HDR to insert cassettes into genes of interest. The cassettes were GFP and CRE into 1 and 2 different genes respectively. This was all done by pronuclear injection into rat zygotes, of RNAs for Cas9 and guide RNA plus circular, double-stranded DNA plasmids containing the cassettes of interest. So this is technically, essentially the same process one would use for mice. Their numbers were quite impressive: between 23% to 54% of live pups carried the targeted insertion.

A key ratio to scrutinize is the ratio of targeted insertions to the total number of insertions and other mutations, e.g. indels. The reason is that the total number reflects the number of pups in which CRISPR clearly had activity. Therefore the ratio reflects the proportion of the time that the HDR process occurred successfully as a subset of all embryos that had some sort of CRISPR-mediated cleavage event. Since almost all of their live pups had evidence of the HDR insertions or indels anyway, the ratio of targeted/all events is still about 25-50%.